IMAC humming power supply? HDD?

Yes I searched the forums before posting this thread, but I could find anything that helped.

Specs of my system: 2.8GHz imac with 750 HDD and 8800 GS

And now the problem, since the update to 1.5.3 (I think I didn't hear it before)
I can hear a low tone humming coming from the area where the hard drive and most likely the power supply is (upper middle of the monitor). The noise is not very loud but the frequency is annoying and it is alternating in a 5 second rhythm (getting louder, disappearing, getting louder...). Because of the frequency I can even hear when watching TV or listening to Music....

It is most likely not the fans since they are running at normal speeds and turning them up to higher speeds does not change anything with the sound (still same level)

It also is not the display humming described in several threads here (I tried changing the brightness and even tuning off the display)

I also tried an SMC reset (turn off pull out all cables and wait 15 secs, I waited a minute just to be sure)

It there anything else I could try? I can't send it in because I really need it?

I've just started to notice it with my iMac last night (3.06ghz / 750g HD / 4g RAM / Nvidia 8800), had it for about a month and a half and because I'd been doing a bit of installing and the like I ran Onyx and pretty much when I restarted the mac I started to notice the humming noise coming from pretty much the same area you described.

Unless I just haven't noticed it before, I did have it close'ish to the wall and I moved it out yesterday to give it a bit more space to breath, suddenly I'm hearing this hum.

I have a feeling it could be something to do with the fans, I have SMC and when I had the fans on my default (1200 / 2100 / 1600) I could make out the hum, it's not that loud but it is noticable, but when I have the fans set to my gaming setting, for Windows XP (2100 / 3200 / 2200) I can't hear it at all, even when I put my ear to the area that it seems to be coming from.

I've started to notice this as well, I suspect that it's been there and I just haven't noticed it as I usually have a window open or iTunes on, just when I had a quiet room that I did realise that the hum was there. It seems to be more noticeable when I have the brightness on my monitor turned down, if it's at full the hum is there but very slight, I really have to listen to hear it or put my ear to the screen (in the centre it's the loudest).

I've checked a few other forums and this seems to be pretty "regular / normal" with the 24" iMacs.

I've only had mine for about a month so I'll put up with it as that is the only issue that I seem to have with my Mac.

If it is coming from the power supply it could be a failing capacitor or one that has minor flaws. This has happened to me on a desktop PC before and though it is annoying, especially if it leaks through the analog audio output making the hum really loud, it may or may not be harmful. If the capacitor has minor flaws but is otherwise fine then no harm should come. However, if the capacitor is failing then your computer can lose power. There may be more serious problems like undervoltage or a power spike either of which could cause more serious damage and data loss.

If it is humming and you are certain it is not a fan or disk drive I would bring it in. Though the repair center may have a lot of background noise making it difficult for the tech to hear the hum.

If it is coming from the power supply it could be a failing capacitor or one that has minor flaws. This has happened to me on a desktop PC before and though it is annoying, especially if it leaks through the analog audio output making the hum really loud, it may or may not be harmful. If the capacitor has minor flaws but is otherwise fine then no harm should come. However, if the capacitor is failing then your computer can lose power. There may be more serious problems like undervoltage or a power spike either of which could cause more serious damage and data loss.

If it is humming and you are certain it is not a fan or disk drive I would bring it in. Though the repair center may have a lot of background noise making it difficult for the tech to hear the hum.

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Thanks for the reply, it seems to be more noticeable in the bottom left hand quarter of the machine (where the glass and alu. meet), if I put my ear to the screen (in the centre) I can hear the hum also but not as much. I did notice that when I have the brightness turned up it does quieten down a bit, but it is still there. I've just become more attune to it now and I seem to listen out for it more!

Is there any way that I can tell if it is something to do with the Power supply without having to take it in? Where I live there is no proper Apple Store, there are a couple of Apple Authorised dealers but I got it from Apple.com so I don't really want to have to send it back, unless I really have to because apart from the noise there is nothing else wrong with my machine.

Thanks again.

I checked my iMac when I got home again and realized that what I said in my last post was not all true, the hum seems to be loudest from about 6 or 7" from the top of the machine vertically and around the middle of the machine horizontally. I put my ear to where the power supply would probably be (the same about area where the plug slots in the back) and the hum is there but not as loud. It is till in the bottom left hand corner of the mac as well, but I have got feeling it is something to do with the display. A friend of mine at work has the previous 24" iMac before this one and he said that he too has got the same sort of humming noise, he's just grown used to it.

As I said, it's not painfully loud, just noticeable when I listen out for it, which is all the time now!

I can confirm this noise on my machine as well. After reading this post I turned my brightness down and noticed it. With the brightness all the way up it is barely noticeable to me but subsequently as its turned down it does get louder. With the number of people confirming this it seems as though this is normal operation.

I'm no wizard with electronic components and circuitry but it seems like a similar situation with the dimmer switches we have installed on several of our overhead incandesent lights at my house. With the dimmer switch in the full on position the lights operate as normal. However, when turning the intensity down the lights tend to produce a ringing or humming noise.

Shorter1, I checked my Mac as well, the sounds seem to be coming from pretty much the same region you suggest, I thought it was around the centre as well, but when I properly checked I did notice it to be more towards the top of the screen. Like yours, the hum is not loud in an annoying sort of way but it is noticeable.

And as klmckenzie03 said, there seem to be a few posts regarding this on a few sites, even the Apple site, that suggest that it's a 'normal' thing with the 24" 3.06g iMac.

Shorter1, I checked my Mac as well, the sounds seem to be coming from pretty much the same region you suggest, I thought it was around the centre as well, but when I properly checked I did notice it to be more towards the top of the screen. Like yours, the hum is not loud in an annoying sort of way but it is noticeable.

And as klmckenzie03 said, there seem to be a few posts regarding this on a few sites, even the Apple site, that suggest that it's a 'normal' thing with the 24" 3.06g iMac.

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Thanks for that, makes me feel a bit better knowing that it's not just me and that it seems to be a common trait with these 24" iMacs, I had a look at the Apple website as well and quite a few people are experiencing the hum noise by the sounds of it.

Going to keep this mac as I have had no problems with it apart from the hum which I 'll get used to anyways.

I`ve been having the same problem with my 3 months old iMac 2.8GHz . The same humming sound from to middle top. A can hear it pulsing every second or so, but when i put it to sleep I hear it disappearing as if it were the fan. The same when it wake up, first the display goes on then the humming starts like a fan.

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